The present invention relates to optical character recognition and, more particularly, to a binary pattern signal producing apparatus for optical character recognition in which a pattern signal delivered from an optical character scanner scanning the surface of a mail article is converted into a binary pattern signal to be supplied to a character recognition unit.
In a flying spot scanner as an example of the optical character scanner, a spot light on the CRT screen is applied to the surface of the mail article through a lens device, and the reflected light from the surface of the mail article is received by a photoelectric transducer such as a photo-multiplier in which address information on the mail article is changed into a corresponding pattern signal. The pattern signal is compared with a predetermined threshold level in order to convert it to a binary pattern signal and the binary pattern signal is then transferred to the character recognition unit. In this case, a level of the pattern signal delivered from the photoelectric transducer changes depending on color or luminance of the surface of the mail article. To cope with this level change problem, the pattern signal from the photoelectric transducer is applied to an amplifier with an automatic gain control (AGC) circuit which keeps the level of the pattern signal substantially constant. The AGC circuit controls the gain of the amplifier in response to the level of the pattern signal such that when the level of the pattern signal is high, the gain is reduced.
In mail articles having windows or labels on their faces, an address is generally written inside the window or on the label. The reflectivity at the window or the label is often lower than that at its surrounding area of the mail article face and sometimes a part of the surrounding area is subjected to scanning together with the window and label. In this case, a pattern signal obtained by the reflected light from the area surrounding the window or the label is dominant over a pattern signal obtained from the window or the label containing the address information, because the reflectivity at the surrounding area is higher than that at the window or the label, and the AGC circuit depends mainly upon the dominant pattern signal corresponding to the area surrounding the window or the label. Therefore, it has often occurred in the prior art binary pattern signal producing apparatus that a binary pattern signal representing the address information cannot be extracted from the pattern signal corresponding to the window or the label containing the address description.
When the window is covered with a transparent film such as cellophane film, the reflected light rays from the transparent film which have an intensity several times larger than that of the reflecting light rays from the surrounding area of the mail face is frequently projected onto the photo-electric transducer, so that impulse noise appears in the pattern signal and the AGC circuit depends upon the high level of the pulse noise which is inevitably adopted as a reference level for AGC. Therefore, the level of the pattern signal corresponding to the address description in the window becomes relatively small and no binary pattern signal representative of address characters and symbols is obtained, resulting in failure of reading the address information in the window. Thus, it is impossible in the prior art apparatus to completely read the address on the mail article which has the window or the label containing the address description.